Yes, agree that the traditional pitot/static system is critical as it relays information required for aircraft performance. However, in the event of icing or system failure GPS information (if somehow made available) could save the day.
I disagree, and this at the "root" of some of the problems we are seeing
Attitude Information is critical - without it we will (in IMC) quickly lose control. Speed is not critical - we can fly all day without it. Altitude / vertical speed depends on circumstances, and certainly loss of Airspeed and Altitude is an issue. However, we do already have GPS altitude as a (somewhat poor) substitute for baro altitude.
What is as critical as Attitude is maintaining lift, which in turns requires an AoA approximation. Hence if we set an appropriate attitude, and have level flight, we know AoA. Or put another way - fly level, and adjust power to get an approximate attitude, we are safe. The basis for any loss of ASI drill.
Trouble is the modern airline environment does not teach or practice attitude flying, but "chasing the Flight Director" and pretending that is Manual Flying
So you say, why not substitute GPS speed for ASI? Well fine, it tells us our speed over the ground, but has zero relevance to lift. Particularly since most of these ASI events seem to icing / CB related, where W/V alters dramatically. At heart is it better to have a "best guess" speed displayed that may well be dangerously wrong? Or remove the "invalid info" and make clear to the pilot it is invalid and they'd better make alternative arrangements.
I am firmly of the belief that "removing" dubious or invalid info is far safer than trying to cobble together a best guess. A read of the AF447 report, and any modern tech manual, I would venture to say shows manufacturers and certification bodies think likewise.
Go back to AF447. Lost ASIs. Had it just been flown level for a short while, ASIs would have reappeared, plug AP back in, carry on. We need to somehow (re)acquire those basic skills.
I reckon most aircraft, setup in the pattern without ASIs, at ~5nu will fly fine (clean), now reduce power, and when attitude hits ~7-8nu take a stage of flap. Will now need return to 3-5nu to fly level and slow again for next stage of flap when required.
When I, or my colleague are practicing a FDs off approach, it is noticeable that typically my colleague will call flaps
purely with regard to the speed annotations (GD, S, F etc.). If the attitude for level flight gets high, and/or there is turbulence, or a turn / level off if I suggest some Flap there is complete confusion as to my concern - even though Alpha Prot has come up
